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  In 1912, Casimir Funk coined the term 'vitamin e' 
to refer to a 'vital factor' he proposed was an essential
component present in foods. His conjecture dovetailed with other
research, leading to the isolation in the 1930's and 40's of the
compounds we now call vitamins. Vitamins are chemical
substances which play a variety of roles in the human body. They
are core components of any nutritional supplementation
program. While many people are aware of vitamins as
necessary substances for good nutrition, few have a grasp of the
extraordinary complexity of the roles they play in our bodies.
As you'll see below, vitamins are involved in trillions of
biochemical interactions every minute to keep us alive and
functioning. For example, B-vitamins are converted into
coenzymes which are directly necessary for the production of ATP
energy from food, a process that goes on continuously in every
cell in the body and which in turn fuels myriad physiological
events such as muscle contraction, brain activity or tissue
repair. Source Naturals offers a full line of vitamins in
bioactive forms, allowing you to tailor a nutritional
supplementation plan to your individual needs. Click here for Vitamin Supplement products ---------------------------------------------------
----------------------------- VITAMIN A and
CAROTENOIDS Vitamin A Vitamin A is a generic term for
a class of fat-soluble substances called retinoids, which can
either be consumed preformed or synthesized by the liver from
plant pigments called carotenoids (see 'Carotenoids', below). An
essential nutrient, vitamin A is perhaps best known for its role
in vision. The outer segments of the rods, a type of
light-sensitive cell in the retina of the eye, contain a pigment
called rhodopsin (or 'visual purple') that mediates vision in
dim light. Cone cells mediate color vision via three additional
pigments. Both rods and cones are surrounded by pigmented
epithelial cells that store vitamin A. Rhodopsin is formed from
a protein called opsin and a vitamin A-dependent compound called
11-cis retinal. As light strikes the rods and cones it is
absorbed by the pigment molecules, and retinal is split off from
opsin. This chemical change allows an electrical impulse to be
sent to the optic nerve and thus to the brain. The pigment must
then be regenerated from opsin and retinal. Repeated small
losses of retinal during this process require a constant
replenishment of vitamin A to the eyes. Vitamin A also
plays an extremely important role in epithelial cell
differentiation. Cell differentiation is the process by which a
cell undergoes a change to a specialized cell type, allowing it
to perform particular functions in the body. It is not yet
understood precisely how vitamin A is involved in this process.
One hypothesis is that it directly affects gene expression
through its interaction with chromatin, a complex of DNA, RNA
and protein in the cell nucleus. These interactions affect the
process of transcription of DNA to messenger RNA, leading to
synthesis of a specific group of cellular proteins. Each
one of us carries in our DNA a unique genetic blueprint. This
genetic material is the same in every cell of our bodies. It is
only because of this mysterious and magical process of
differentiation that we have specialized cell types - and
therefore eyes, ears, lungs and hearts. Vitamin A is
necessary, either directly or indirectly, for the healthy growth
and functioning of many of our tissues and organ systems,
including the eyes, the skin, the bones, the reproductive
system, and the natural defenses. It is not yet known whether
this requirement is due to the role of vitamin A in cell
differentiation or whether there are other physiological
processes for which vitamin A is essential. Carotenoids
Vitamin A is related to a class of nutrients called carotenoids,
including alpha and beta carotene, lycopene and lutein.
Carotenoids are botanical pigments whose colors range from red
to orange to yellow. Some carotenoids, particularly beta
carotene, can be converted into vitamin A predominantly in the
intestinal mucosa and to some extent in the liver. Carotenoids
are completely non-toxic; their conversion into vitamin A is
well-regulated by the body, making them extremely safe sources
of this essential nutrient. In addition to their role as
safe sources of vitamin A, carotenoids are powerful nutrients in
their own right. Their primary claim to fame is their powerful
antioxidant action, particularly against singlet oxygen. Singlet
oxygen is an 'excited' ion of oxygen which, while not
technically a free radical, is nonetheless highly reactive. It
causes 'oxidative' reactions which can impair or destroy
membranes, enzymes and DNA. It can also lead to the formation of
free radicals which can cause additional damage. Certain
carotenoids such as beta carotene, because of their chemical
structure, can neutralize singlet oxygen by absorbing its extra
energy and dissipating it throughout the carotenoid molecule,
releasing the energy as heat and converting the singlet oxygen
back to 'normal' oxygen. One molecule of beta carotene can
quench up to 1000 molecules of singlet oxygen. In
addition to their role as singlet oxygen quenchers, carotenes
provide antioxidant protection against free radicals as well. In
nature, they protect plants from photo-oxidative reactions; in
humans, certain carotenoids, notably beta carotene, may help
protect the skin from such reactions. Other carotenoids may
provide more localized protection to particular organs. Lutein
and zeaxanthin, for example, are selectively concentrated in the
retina of the eye. Along with vitamins C and E, carotenes are
among the most important nutrient antioxidants in the human

VITAMIN, A, and,